When they pointed the antenna at empty patches of sky, the researchers stumbled on a low-level hiss. The constant noise would turn out to be cosmic radiation—cosmic microwave background—evidence for the Big Bang theory of the beginning of the universe.

The Big Bang theory suggests that the universe was once hotter than the surface of the Sun and emitted bright light. If this was the case, we should be able to detect the radiation from that early expansion of the universe—which Wilson and Penzias were the first to do, on that May day 50 years ago.

Learn more about this monumental discovery in a video:

Learn more about cosmic microwave background and other pivotal discoveries about our universe in Dark Universe, the new Space Show narrated by Neil deGrasse Tyson.